1. Field of the Invention
This invention relates to a hydraulic jack and in particular to a toe jack.
2. Discussion of the Prior Art
So-called toe jacks are by no means new. In this connection reference is made to U.S. Pat. No. 2,165,367, issued to F. L. Gormley et al on Jul. 11, 1939; U.S. Pat. No. 2,412,414, issued to J. J. Mueller on Dec. 10, 1946; U.S. Pat. No. 2,469,670, issued to C. L. Thompson on May 10, 1949; U.S. Pat. No. 2,654,568, issued to W. S. Pine on Oct. 6, 1953; U.S. Pat. No. 3,081,066, issued to S. A. Murawski on March 12, 1963; U.S. Pat. No. 3,622,124, issued to K. R. Sidles et al on Nov. 23, 1971; U.S. Pat. No. 4,174,095, issued to D. L. Chipman on Nov. 13, 1979; U.S. Pat. No. 4,886,244, issued to J. Renault on Dec. 12, 1989; U.S. Pat. No. 5,048,794, issued to M. Mamessier on Sept. 17, 1991 and U.S. Pat. No. 5,524,868, issued to A. F. Decker et al on Jun. 11, 1996.
In general, existing jacks of the type in question suffer from a major problem, namely they operate at one speed. When the jack is placed under a load, it is often necessary to pump for a relatively long time before the load lifting element of the jack reaches the load. Because the load lifting element rises in small increments regardless of whether it is in engagement with the load, the pumping action must be repeated many times before the load is actually engaged and lifting starts.
Some jacks include a base, a piston securely mounted on the base, a load carrying cylinder mounted on the piston for vertical movement relative to the piston and base, and a pump body and a hydraulic fluid reservoir mounted on the cylinder. A handle connected to the pump body is used to pump hydraulic fluid from the reservoir to the cylinder. Thus, during pumping, the cylinder, the reservoir and the pump handle move upwardly as a unit with a load.
An object of the present invention is to provide a relatively simple two-speed toe jack, i.e. a jack with load engaging elements which can be moved rapidly upwardly into engagement with a load and then slowly while lifting the load.
Another object of the invention is to provide a simple toe jack the bulk of which is fixedly mounted on a base, with only a piston or plunger and load carrying elements moving during a lifting operation. Thus, the center of gravity of the jack remains low, and when the jack is raised it does not become top heavy.
Accordingly, the invention relates to a hydraulic toe jack comprising:
(a) a base for supporting the jack on a support surface;
(b) a reservoir on said base for hydraulic fluid;
(c) a main cylinder on said base for receiving hydraulic fluid from said reservoir,
(d) a plunger in said main cylinder for vertical movement relative to said base, said reservoir and said main cylinder;
(e) a load carrying sleeve on said plunger for vertical movement therewith;
(f) a toe on said sleeve for engaging a load; and
(g) a two-stage pump on said base for pumping hydraulic fluid from said reservoir to said main cylinder at high volume and low pressure and at low volume and high pressure, whereby, during a pumping operation, the plunger and load carrying sleeve can be moved rapidly upwardly to engage a load and once in engagement with the load is moved slowly upwardly under high pressure.